The present invention relates to a process for producing highly pure rhamnose from gum arabic.
Rhamnose is present in nature as a saccharide component of glycosides such as rutin (containing 26.8% by weight of rhamnose), hesperidin (containing 29.5% by weight of rhamnose), quercitrin (containing 40% by weight of rhamnose), myricitrin and naringin, and as a saccharide constructing gum arabic.
Hitherto, the production of rhamnose has been effected by hydrolyzing one of the above-mentioned glycosides of a high content of rhamnose, however, it is difficult from the view point of amount and cost to supply rhamnose as the industrial starting material because of the small production of the above-mentioned glycosides and the high price thereof.
In addition, in the case of using rutin as the starting material, contamination by quercetin which is suspected of carcinogenesis is considered and accordingly rhamnose from rutin is not desirable in its use.
Although as an another method of producing rhamnose, a process comprising culturing a species of bacteria belonging to the genus Pseudomonas, thereby obtaining a rhamnolipid produced by the bacteria and producing rhamnose from the rhamnolipid has also been known, the productivity of rhamnose by the process is not necessarily satisfactory.
In consideration of the above-mentioned situation, the object of the present invention is to provide a process for producing rhamnose of a high purity at a high efficiency from gum arabic which is available in a relatively large amount in nature as a rhamnose-containing substance.
Gum arabic is a substance secreted from the trunks of a leguminous plant belonging to the genus Acacia, and is utilized commercially in a broad field. Particularly, since gum arabic has been used as a stabilizer and an emulsifier of foods and medicines for a long time and there has been no problem in its safety in human life, there is a merit that rhamnose produced from gum arabic can be used without any restriction. The major component of gum arabic comprises lysaccharides of presumed structural formulae, generally composed mainly of galactose while being accompanied by arabinose, rhamnose, glucuronic acid, etc. and it is considered that rhamnose is present as the saccharide at the molecular end of gum arabic.
As a result of the present inventors' studies for the process of hydrolyzing gum arabic and the method for treatment of the liquid hydrolyzate of gum arabic, it has been made possible by the present inventors to increase the amount of rhamnose in the total amount of the monosaccharides obtained by hydrolysis of gum arabic, to improve the efficiency for separating rhamnose from the hydrolyzate and to obtain rhamnose of a high purity, and based on the present inventors' findings the present invention has been attained.